This invention relates to infrared countermeasures systems and more particularly to multipulse infrared countermeasures systems.
Modulated infrared sources are employed to countermeasure heat seeking missiles which home in on the heat generating portions of a target such as the engines of an airplane or helicopter. Certain of such systems provide a counter measuring signal to a heat seeking missile through spatial modulation by sweeping a beam in space. Reflective optics are rotated about a source of infrared radiation such that the missile receives a pulse of energy each time the beam passes the missile.
While illuminating the missile with single pulses of infrared radiation provides an effective countermeasure against the missile, it has been determined that better protection can be afforded by periodically illuminating the missile with bursts of pulses rather than single pulses. Prior to the present invention, the only method of obtaining pulse bursts was to provide concentric modulators driven at different speeds wherein a source is modulated by a first modulator and the output of the first modulator is further modulated by a second modulator. While this system performs more than adequately, it is limited in the amount of achievable gain, since the output from the first modulator is not reimaged prior to being applied to the second modulator. Furthermore, this system requires multiple drives since the modulators must be run at different speeds to achieve multipulse operation. This later system is disclosed in U.S. patent application Ser. No. 543, 299, filed by the inventors of this application on Jan. 20, 1975, and is assigned to the assignee of the present application.